Such components may be configured, for example, as connecting rods having a small connecting rod eye, a shaft and a large connecting rod eye, wherein the large connecting rod eye is provided with a split bearing seat for supporting the connecting rod at the crankshaft. Since the invention relates in particular to the production of a connecting rod, the discussion below is devoted primarily to a connecting rod, but only by way of example and not by way of limitation.
A connecting rod is generally produced in that first a preform is produced, e.g., by means of forging, casting or powder-metallurgy methods, with the inside dimension of the large connecting rod eye having an oversize in the region of the future separation location. At this location the large connecting rod is separated, e.g., by means of sawing, thus extensively eliminating the oversize. The separation surfaces of the connecting rod cap formed in this manner, on the one hand, and of the remainder of the connecting rod on the other are processed in a further method step, e.g., by means of grinding, so as to fit together precisely. In its finished state, the connecting rod cap is attached to the remainder of the connecting rod by means of connecting rod screws; the screw holes required for this purpose may be bored before or after separation. In the assembled state of the connecting rod, the mechanical processing of the bearing seat is subsequently effected to receive bearing shell halves, which are disposed between connecting rod and crankshaft, forming a friction bearing.
Another method of separating the connecting rod cap from the remainder of the connecting rod is known from DE-PS 38 06 236, where the connecting rod cap is separated from the remainder of the connecting rod by means of fracture separation. During this process, a fracture surface having a large, irregular surface is produced as separation surface, which almost excludes a lateral displacement of the connecting rod cap on the remainder of the connecting rod. This accomplishes, on the one hand, that the fastening of the bearing shells in the bearing seat of the connecting rod is improved and, on the other hand, that only the respective connecting rod cap that has been separated can be attached to the respective remainder of the connecting rod because the fracture surface is unique. A confusion of individual parts, e.g., during assembly or repair of the motor, is thus ruled out.
Depending on the configuration of the motor, it may be advisable or even necessary to provide an antifriction bearing arrangement, particularly via needle roller bearings, instead of the friction bearing of the connecting rod at the crankshaft that is usually used. This is the case, for example, in large-volume motors or in miniature motors.
If rolling elements are arranged between crankshaft and connecting rod, it is necessary for the outer running face, this means the running face disposed on the connecting rod, to also have a high degree of hardness in order to withstand the constant stress of the rolling elements. Furthermore, it is necessary for assembly reasons that this running face also be configured as a split running face. The use of customary bearing shell halves or of correspondingly configured outer bearing races for the rolling elements is therefore not easily possible. In addition, the simultaneous use of rolling elements on the one hand and a split outer bearing race on the other would increase the physical dimensions of the connecting rod and thus of the material mass that can be moved back and forth inside the motor and thus the weight of the motor, which, inter alia, would have an unfavorable influence on the motor's fuel consumption.
It is possible to provide the bearing seat surfaces of the split bearing seat with a hardness suitable for antifriction bearings, e.g., by means of skin layer hardening. However the materials used for the manufacture of the connecting rods do not have the required carbon content, since an increased carbon content is an obstacle to reshaping as well as mechanical processing. Therefore, it is necessary that, prior to the skin layer hardening, such connecting rods be carburized in a carbon-containing atmosphere. In this process, it must be taken into account that, owing to the special stress on the connecting rod, carburization should only take place in the region of the running face, which means that complex preparatory measures must be taken to avoid carburization of the skin layer of the remainder of the connecting rod.
A further problem during the manufacture of a component with a split running face for rolling elements is that the rolling elements move over the separation location between the bearing cap and the remainder of the connecting rod during each turning movement. Even with the most careful mechanical processing it cannot be ruled out that the separation location will remain in existence in the form of a minimal separation line. Furthermore, there is the risk that the separation line is made larger because of lateral displacement of the bearing cap on the remainder of the component after assembly, both in the radial and in the axial direction, so that the running face no longer has a planar configuration. As a result of both phenomena, premature wear of the rolling elements must be expected, which may lead to motor failure.
The object of the invention is to create a method of producing a component having at least one split running face for rolling elements in which the above-named disadvantages are avoided to the greatest possible extent. Additionally, the implementation of the method should be simple and cost-effective.